Nerve growth factor prevents arsenic-induced toxicity in PC12 cells through the AKT/GSK-3β/NFAT pathway

The potential risk of arsenic-related neurodegeneration has been a growing concern. Arsenic exposure has been reported to disrupt neurite growth and neuron body integrity in vitro; however, its underlying mechanism remains unclear. Previously, we showed that arsenic sulfide (AS) exerted cytotoxicity in gastric and colon cancer cells through regulating nuclear factor of the activated T cells (NFAT) pathway. The NFAT pathway regulates axon path finding and neural development. Using neural crest cell line PC12 cells as a model, here we show that AS caused mitochondrial membrane potential collapse, reactive oxygen species production, and cytochrome c release, leading to mitochondria-mediated apoptosis via the AKT/GSK-3β/NFAT pathway. Increased glycogen synthase kinase-3 beta (GSK-3β) activation leads to the inactivation of NFAT and its antiapoptotic effects. Through inhibiting GSK-3β activity, both nerve growth factor (NGF) and Tideglusib, a GSK-3β inhibitor partially rescued the PC12 cells from the AS-induced cytotoxicity and restored the expression of NFATc3. In addition, overexpression of NFATc3 stimulated neurite outgrowth and potentiated the effect of NGF on promoting the neurite outgrowth. Collectively, our results show that NFATc3 serves as the downstream target of NGF and plays a key role in preventing AS-induced neurotoxicity through regulating the AKT/GSK-3β/NFAT pathway in PC12 cells.     

Calcineurin-NFATc signaling pathway regulates AQP2 expression in response to calcium signals and osmotic stress

The aquaporin (AQP)2 channel mediates the reabsorption of water in renal collecting ducts in response to arginine vasopressin (AVP) and hypertonicity. Here we show that AQP2 expression is induced not only by the tonicity-responsive enhancer binding protein (TonEBP)/nuclear factor of activated T cells (NFAT)5-mediated hypertonic stress response but also by the calcium-dependent calcineurin-NFATc pathway. The induction of AQP2 expression by the calcineurin-NFATc pathway can occur in the absence of TonEBP/NFAT5. Mutational and chromatin immunoprecipitation analyses revealed the existence of functional NFAT binding sites within the proximal AQP2 promoter responsible for regulation of AQP2 by NFATc proteins and TonEBP/NFAT5. Contrary to the notion that TonEBP/NFAT5 is the only Rel/NFAT family member regulated by tonicity, we found that hypertonicity promotes the nuclear translocation of NFATc proteins for the subsequent induction of AQP2 expression. Calcineurin activity was also found to be involved in the induction of TonEBP/NFAT5 expression by hypertonicity, thus further defining the signaling mechanisms that underlie the TonEBP/NFAT5 osmotic stress response pathway. The coordinate regulation of AQP2 expression by both osmotic stress and calcium signaling appears to provide a means to integrate diverse extracellular signals into optimal cellular responses. aquaporin; nuclear factor of activated T cells; tonicity-responsive enhancer binding protein; osmotic response